The present invention relates to an electrostatic air cleaner and, more particularly, to an air cleaner which is suitable for removing smoke and the like mixed in the air.
An electrostatic air cleaner generally employed in the past is separated into an ionization region for charging positive particles of dust, smoke and so forth mixed in the air and a collector region for adsorbing positively charged particles on a negatively charged plate. The ionization region is formed by a thin wire disposed between opposing metal plates and the thin wire is selected from metals having the property of releasing free ions (+) in quantities when supplied with a voltage, such as tungsten. The metal plates, which surround the thin wire in spaced relation thereto, are formed of a metal having the property of attracting the (+) ions when supplied with a negative voltage. On the other hand, the collector region is usually formed by a series of aluminum plates, and these plates are adapted to be supplied with positive and negative voltages alternately.
The efficiency of the electrostatic air cleaner of this kind is dependent on the degree of ionization in the ionization region and the strength of the attractive force in the collector region. The degree of ionization can be raised through the use of a thin wire having the property of releasing free ions (+) in quantities as referred to above more effective means therefor is to increase the voltage that is applied to the ionization region. Likewise, the attractive force in the collector region can markedly be increased by raising the voltage to be applied thereto other than the selection of the material used. The spacing of the metal plates in the collector region affects the attractive force, which is increased by reducing their spacing.
While, in view of the above, it may appear that the efficiency of the prior art electrostatic air cleaner could easily be improved by raising the voltage applied, there is a limit to the voltage increase owing to such problems as sparking and the generation of ozone that is bad for the health even in small quantities. Therefore, it is necessary that the voltage used be selected sufficiently low not to allow the generation of sparks between the metal plates and the formation of ozone in the collector region.
A method that is now employed for promoting the ionization is to leave a wide space between the tungsten thin wire and the metal plates for the application of a high voltage. At present, however, the voltage cannot be raised above a predetermined value because of preventing the generation of ozone. If ionization were promoted, then the dust collecting and smoke removing efficiency could be increased through using a voltage low enough to prevent spark generation in the collector region.
As described above, the conventional electrostatic air cleaner is low in efficiency on account of the requirement that the voltage be held below a predetermined value for avoiding the generation of sparks and ozone.
Another problem that has been encountered in the past is that the electrode plates forming the ionization region and the collector region must be washed after use for a predetermined period of time, since it is excessively uneconomical to make disposable the electrode plates formed by aluminum or like metal plates. In addition, since nicotine, tar and so forth contained in tobacco smoke adhere to the electrode plates, it is extremely difficult to remove them by ordinary washing.
In view of such problems as mentioned above, the object of the present invention is to provide an electrostatic air cleaner which overcomes the efficiency limitations imposed on the prior art and permits the use of relatively low-priced disposable electrode plates.
After experimental research on the materials of collector plates used in conventional electrostatic air cleaners of the abovesaid type, the present inventor found that plates formed of various nonconductive materials and nonmetallic materials which, contrary to the customary ideas regarding conductive collector plates, have a surface potential equal to or higher than does an aluminum plate may be employed and, based on this finding, he has now completed the present invention.